Role of aberrant sialylation of chronic myeloid leukemia granulocytes on binding and signal transduction by chemotactic peptides and colony stimulating factors

When Glycosylation Meets Blood Cells: A Glance of the Aberrant Glycosylation in Hematological Malignancies

Among neoplasia-associated epigenetic alterations, changes in cellular glycosylation have recently received attention as a key component of hematological malignancy progression. Alterations in glycosylation appear to not only directly impact cell growth and survival, but also alter the adhesion of tumor cells and their interactions with the microenvironment, facilitating cancer-induced immunomodulation and eventual metastasis. Changes in glycosylation arise from altered expression of glycosyltransferases, enzymes that catalyze the transfer of saccharide moieties to a wide range of acceptor substrates, such as proteins, lipids, and other saccharides in the endoplasmic reticulum (ER) and Golgi apparatus. Novel glycan structures in hematological malignancies represent new targets for the diagnosis and treatment of blood diseases. This review summarizes studies of the aberrant expression of glycans commonly found in hematological malignancies and their potential mechanisms and defines the specific roles of glycans as drivers or passengers in the development of hematological malignancies.

CD15 expression in human myeloid cell differentiation is regulated by sialidase activity

The glycan determinant CD15 (also known as Lewis x, or Le(x)) is a distinguishing marker for human myeloid cells and mediates neutrophil adhesion to dendritic cells. Despite broad interest in this structure, the mechanisms underlying CD15 expression remain relatively uncharacterized. Accordingly, we investigated the molecular basis of increasing CD15 expression associated with human myeloid cell differentiation. Flow cytometric analysis of differentiating cells together with biochemical studies using inhibitors of glycan synthesis and of sialidases showed that increased CD15 expression is not due to de novo biosynthesis of CD15, but results predominantly from induction of alpha(2-3)-sialidase activity, which yields CD15 from cell-surface sialyl-CD15 (also known as sialyl-Lewis x, sLe(x) or CD15s). This differentiation-associated conversion of surface CD15s to CD15 occurs mainly on glycoproteins. Until now, modulation of post-translational glycan modifications has been attributed solely to dynamic variations in glycosyltransferase expression. Our results unveil a new paradigm by demonstrating a critical role for post-Golgi membrane glycosidase activity in the 'biosynthesis' of a key glycan determinant.

Expression of sialyltransferase activity on intact human neutrophils

Endogenous polymorphonuclear leukocyte (PMN)-associated sialidase activity enhances PMN adhesion to and migration across the endothelium through the removal of sialylated cell-surface residues. We tested the hypothesis that PMNs also express sialyltransferase (ST) activity that restores sialyl residues to the PMN surface. We developed a highly sensitive fluorometric assay to demonstrate that intact human PMNs can mediate and accept sialyl residue transfer. This ST activity is inhibited by a ST inhibitor, CMP, which also inhibits the transendothelial migration of PMNs in response to IL-8 in vitro and in vivo. We conclude that intact PMNs express sialidase and ST activities that permit rapid modulation of their surface sialylation and their ability to adhere to and migrate across the endothelium.

Serum total sialic acid in cholangiocarcinoma patients: an ROC curve analysis

OBJECTIVES

This study was undertaken to establish the diagnostic utility of serum total sialic acid (TSA) for patients with cholangiocarcinoma (CCA).

DESIGN AND METHODS

Serum TSA was determined in 89 histologically confirmed CCA patients, 38 with benign hepatobiliary diseases (BHD) and 43 healthy persons. To check whether the test could adequately discriminate between these groups, complete statistical Receiver Operating Characteristic (ROC) curves were analyzed.

RESULTS

The mean value of serum TSA in CCA patients (2.75 +/- 0.67 mmol/L) was significantly higher than that in the BHD (2.33 +/- 0.69 mmol/L p < 0.002) and healthy persons (1.89 +/- 0.46 mmol/L p < 0.001) groups. The areas under the ROC curves were 0.6699 and 0.8558, respectively. A cut-off value of 2.33 mmol/L discriminated between the CCA, BHD and healthy groups with a sensitivity of 71.9% and a positive predictive value range of 80 to 89%.

CONCLUSION

Determination of TSA yielded high diagnostic values for differentiating between CCA, BHD and healthy persons. The determination of serum TSA would be most useful as an adjunct diagnosis rather than an early detection and screening tool because of the apparent nonspecificity of SA to a given disease.

Occurrence of sialic acids in healthy humans and different disorders

Sialic acid (SA), N-acetylated derivatives of neuraminic acid, play a central role in the biomedical functioning of humans. The normal range of total sialic acid (TSA) level in serum/plasma is 1.58-2.22 mmol L-1, the free form of SA only constituting 0.5-3 mumol L-1 and the lipid-associated (LSA) forms 10-50 mumol L-1. Notably, considerably higher amounts of free SA are found in urine than in serum/plasma (approximately 50% of the total SA). In inherited SA storage diseases such as Salla's disease, SA levels are elevated many times over, and their determination during clinical investigation is well established. Furthermore, a number of reports describe elevated SA levels in various other diseases, tentatively suggesting broader clinical utility for SA markers. Increased SA concentrations have been reported during inflammatory processes, probably resulting from increased levels of richly sialylated acute-phase glycoproteins. A connection between increased SA levels and elevated stroke and cardiovascular mortality risk has also been reported. In addition, SA levels are slightly increased in cancer, positively correlating with the degree of metastasis, as well as in alcohol abuse, diabetes, chronic renal failure and chronic glomerulonephritis. Several different mechanisms are assumed to underlie the elevated SA concentrations in these disorders. The apparent non-specificity of SA to a given disease limits the potential clinical usefulness of SA determination. In addition, some non-pathological factors, such as aging, pregnancy and smoking, may cause changes in SA concentrations. The absolute increases in SA levels are also rather small (save those in inherited SA storage disorders); this further limits the clinical potential of SA as a marker. Tentatively, SA markers might serve as adjuncts, when combined with other markers, in disease screening, disease progression follow-up, and in the monitoring of treatment response. To become clinically useful, however, the existing SA determination assays need to be considerably refined to reduce interferences, to be specific for certain SA forms, and to be more easy to use.